Effect of Laser Ablation on Microwave Attenuation Properties of Diamond Films

Abstract

Thermal conductivity is required for developing high-power microwave technology. Diamond has the highest thermal conductivity in nature. In this study, a diamond film was synthesized by microwave plasma chemical deposition, and then long and short conductive graphite fibers were introduced to the diamond films by laser ablation. The permittivity of the samples in the K-band was measured using the transmission/reflection method. The permittivity of diamond films with short graphite fibers increased. The increase in real part of permittivity can be attributed to electron polarization, and the increase in the imaginary part can be ascribed to both polarization and electrical conductivity. The diamond films with long graphite fibers exhibited a highly pronounced anisotropy for microwave. The calculation of microwave absorption shows that reflection loss values exceeding −10 dB can be obtained in the frequency range of 21.3–23.5 GHz when the graphite fiber length is 0.7 mm and the sample thickness is 2.5 mm. Therefore, diamond films can be developed into a microwave attenuation material with extremely high thermal conductivity.

Microstructures Manufactured in Diamond by Use of Laser Micromachining

“…Nano-pattering of diamond surfaces in high resolution (single atoms scale) was created by the graphite-free laser etching of diamond using 266 nm laser pulses [15,16]. Recently, Ding et al [17] have shown that diamond films modified with laser ablation could be developed into a microwave attenuation material by obtaining the graphite fibers within diamond. Other applications, which have been implemented recently, are described in the review article by Truccchi at al [18].…”

Multifunctional Composite Material with Efficient Microwave Absorption and Ultra-High Thermal Conductivity

“…Specifically, Zhang et al [11] used carbon fibers to establish microscopic thermal conduction pathways, making the thermal conductivity of the material as high as 15.55 W•m −1 •K −1 , which is the polymer-based HC-EMWAMs with the highest thermal conductivity reported in the literature. Subsequently, some researchers replaced the polymer substrate by materials with high thermal conductivity [13][14][15][16][17][18][19][20][21][22] and then added lossy filler to prepare ceramics with high thermal conductivity and strong microwave absorption. These approaches have the potential to enhance mechanical properties, wave absorption, and superhigh thermal conductivity of materials, most of them are greater than 70 W•m −1 •K −1 .…”